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Chapter 7-5 - Nomenclature of Cis-Trans Isomers
Organic Chemistry 307: Chapter 7 - Structure and Synthesis of Alkenes; Section 5 - Nomenclature of Cis-Trans Isomers
Organic Chemistry
Undergraduate 3

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The rigidity and lack of rotation of carbon-carbon double bonds gives rise to __________-__________ isomerism, also called __________ isomerism.
1) Cis-trans
2) Geometric
If two similar groups bonded to the carbons of a double bond are on the same side of the bond, the alkene is a __________ isomer.
If the similar groups are on opposite sides of the bond, the alkene is __________.
1) Cis
2) Trans
Not every alkene is capable of __________-__________ isomerism; if either carbon of the double bond holds two __________ groups, the molecule cannot show cis-trans isomerism.
1) Cis-trans
2) Identical
__________ cycloalkenes are unstable unless the ring is large enough (at least __________ carbon atoms) to accommodate the __________ double bond.
1) Trans
2) Eight
3) Trans
All cycloalkenes assumed to be __________ unless they are specifically named trans.
1) Cis
The __________ name is rarely used with cycloalkanes, except to distinguish a large cycloalkene from its trans isomer.
1) Cis
The __________ __________ of nomenclature for cis-trans isomers is patterned after the __________-__________-__________ convention for asymmetric carbon atoms and is used to distinguish between isomers which may often have an ambiguous name.
1) E-Z System
2) Cahn-Ingold-Prelog
Naming an Alkene with the E-Z System:
1. Mentally separate the double bond into two ends.
2. Consider each end of the double bond separately, and use the __________-__________-__________ rules to assign first and second priorities to the two substituents on that end.
3. Do the same for the other end of the double bond.
If the two first-priority atoms are together (__________) on the same side of the double bond, you have the __________ isomer.
If the two first-priority atoms are on opposite (__________) sides of the double bond, you have the __________ isomer.
1) Cahn-Ingold-Prelog
2) Cis
3) Z (for zusammen, "together")
D) Trans
5) E (for entgegen, "opposite")
*Rules for Naming Alkenes*
1. Select the longest chain or largest ring that contains the largest possible number of __________ __________, and name it with the __________ suffix.
2. Number the chain from the end __________ to the double bonds. Number a ring so that the double bond is between carbons __________ and __________.
3. Name substituent groups as in alkanes, indicating their locations by the number of the main-chain carbon to which they are attached. The ethenyl and propenyl group are usually called the __________ and __________ group, respectively.
4. For compounds that show __________ isomerism, add the appropriate prefix: __________ or __________ or __________ or __________. Cycloalkenes are assumed to be __________ unless named otherwise.
1A) Double bond
1B) -ene
2A) Closest
2B) One
2C) Two
3A) Vinyl
3B) Allyl
4A) Geometric
4B) Cis
4C) Trans
4D) E
4E) Z
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